An advantageous method for interconnection of multiple integrated circuits on modules is known as High Density Interconnect (HDI). In this arrangement for interconnection of integrated circuits, generally speaking, wells are defined in the module, which accept the various integrated circuit chips, and which hold the chips with their upper surfaces coplanar. The metallized contacts or terminals on the upper surfaces are then interconnected in the desired manner by thin, flexible, printed-circuit sheets. Interconnections between the layers of the printed-circuit sheets, and between the circuits on the sheets and the terminals on the integrated-circuit chips, are accomplished by way of metallized vias. Such HDI modules have various advantages, including good heat-sinking of the integrated-circuit chips, and the possibility of repair of a module in which one chip is bad, by stripping off the interconnecting sheet, replacing the defective chip, and replacing the chip interconnections by use of the same, or a new interconnection sheet.
Many HDI modules are intended for use in adverse environments, in which it is desired that the module be hermetically sealed against environmental factors. This means that the interconnections between the circuits within the module and the outside world must occur in a hermetic fashion. In some applications, the signals applied to the HDI module, or the signals leaving the HDI module, may be at sufficiently high frequencies that distributed reactances have effects on the signal transmission. Those skilled in the art know that the appropriate way to transport signals at such high frequencies is the use of distributed transmission lines having substantially constant characteristic impedances along their lengths, or if the impedances along their lengths vary, by the use of appropriate impedance transformations. It should be noted that the term "high frequency" in this context is technology-sensitive, in that in the early days of radio, frequencies in the range of 550 to 1600 kilocycles per second (kc or KHz) would have been considered to be difficult to work with because of distributed effects, while with current technology and its very small components, such effects are considered to be relatively small below about 50 MHz, except possibly for special purposes.
Improved devices and/or methods for making hermetic high-frequency connections between elements and chips inside an HDI module and the world external to the HDI module are desired.